1. Field
One embodiment of the invention relates to a portable terminal capable of performing location measurement using a GPS function.
2. Description of the Related Art
There is a wristwatch type positioning device which measures a location using a GPS (for example, see JP-A-2002-243832 (Paragraph Number 0027 to 0042 and FIGS. 4 to 6)). The positioning device is operated in a precision priority measurement mode in which precision is higher than that of a one-time measurement mode. A GPS module 8 of the positioning device measures a DOP (Dilution of Precision) value indicating location measurement for calculating a present location and precision of the location measurement on satellite data.
In a second embodiment, the DOP value desired beforehand by a user and continuous time of successive positioning are input in the precision priority measurement mode. In addition, the positioning device searches satellites within the range of the continuous time and calculates the location measurement and the DOP value on the basis of the satellite data to display the DOP value on a precision indicator 100. In addition, the positioning device displays longitude and latitude of the location measurement measured on a display unit 12 when the calculated DOP value is equal to or less than the desired DOP value, and turns off the GPS module to terminate the positioning process. In addition, when the continuous time of the successive positioning ends, the GPS module is turned off to terminate the positioning process. In this way, the positioning process with the precision desired by the user can be performed and unnecessary power consumption can be suppressed.
The positioning device disclosed in JP-A-2002-243832 calculates the DOP indicating the precision of the location measurement. The DOP is theoretical precision which is determined on the basis of the number of satellites received by the positioning device or the geometric arrangement of the satellites. The present location of the positioning device determined by the positioning device is determined by the theoretical precision of the DOP and factors unrelated to the DOP including indefinite imbalance factors and the like caused due to an error of reflection and the like on buildings where the positioning device is located.
Accordingly, in the positioning device disclosed in JP-A-2002-243832, there is a situation that the calculated DOP value becomes a value equal to or less than a desired DOP value, that is, the location measurement at the moment when the theoretical precision is good does not necessarily have high precision and may have much error.